Oleophilic metals



3,532,623 OLEOPHILIC METALS Aleksander Jerzy Groszek, London, England,assignor to The British Petroleum Company Limited, London, England NoDrawing. Filed Mar. 5, 1969, Ser. No. 804,667 Claims priority,application Great Britain, Mar. 7, 1968, 11,109/ 68 Int. Cl. C10m /02US. Cl. 25226 3 Claims ABSTRACT OF THE DISCLOSURE Metal flakes having ahigh surface area of at least 1 square metre per gram produced bygrinding metals in an organic liquid can thicken lubricating oils togreases.

This invention relates to compositions containing metal flakes moreparticularly it relates to liquids having metal flakes dispersedtherein.

1 have now found that compositions incorporating metal flakes, and whichhave a high surface energy, high surface area and low bulk density, havemany useful properties.

The present invention provides a composition comprising a liquiddispersion medium having dispersed therein metal flakes having a surfaceenergy of at least 0.01 calorie per gram, a surface area of at least 1square metre per gram and a bulk density of less than 1 gram per cc.

The metal flakes which are useful in the present invention can beprepared by grinding a metal in an organic liquid (hereinafter referredto as the organic grinding liquid) in the presence of a grinding aidsuch as a loadcarrying additive for lubricants. Preferably a high energymill such as a vibration ball mill of vibrational amplitude of at least2 mm. and a vibration frequency of at least 500 cycles a minute is used.

The organic liquids used as the grinding medium include hydrocarbonsespecially n-heptane, iso-octane, cyclohexane, toluene, hexadecane or ahydrocarbon fraction obtained by the distillation of petroleum. Otherliquids which can be used include most volatile oxygen-, halogen-,nitrogen-, and sulphur-containing liquids. Preferably the grindingliquids have a surface tension less than 72 dynes/ cm. more preferablyless than 45 dynes/cm. at 25 C. The viscosity of the liquid at thegrinding temperature must be sufliciently low to enable the grindingaction to be sufficiently energetic to produce a metal powder having thedesired surface energy, surface area and bulk density, for this reasonliquids with a viscosity of less than 30 centistokes, more preferablyless than 3 centistokes and most preferably less than 1 centistoke at100 F. are preferred.

By grinding aid is meant a compound which facilitates grinding and isselected from load-carrying additives for lubricants, fatty acids, fattyacid esters and fatty alcohols.

The grinding liquid can contain any conventional loadcarrying additivefor lubricants. Lubricant load-carrying additives are usually compoundscontaining one or more elements of Groups 5, 6 or 7 of the PeriodicTable especially nitrogen, phosphorus, sulphur and chlorine. Thegrinding liquids may also contain, as a grinding aid, a fatty alcohol,fatty acid or ester thereof either in addition to the load-carryingadditive or in its place. In general the better the lubricating activityof the additive or acid on the unground metal the more effective it willbe in the grinding process. The preferred load-carrying additive iscarbon tetra-chloride and the preferred fatty acids are stearic acid,palmitic acid or their vinyl esters. Cetyl alcohol may also be used.

Suitable metals which can be used in the present invensates mm tioninclude the transition metals, especially iron, aluminium, copper, zinc,tin and lead. Alloys such as cast iron, steel and brass may also beused.

The grinding preferably takes place in the substantial absence of airand more preferably the metal is below the surface of the grindingliquid for the duration of the grinding.

Preferably the metal flakes used in the present invention have a surfaceenergy of at least 0.05 calorie per gram, a surface area of at least 2square metres per gram and a bulk density of less than 0.5 gram per cc.In some cases surface energies of more than 10 calories per gram and ashigh as calories per gram can be obtained.

The surface energy of the metal flakes can be determined using the flowmicro-calorimeter as described in Chemistry and Industry March 20, 1965,pp. 482-489, using n-butanol adsorbed from n-heptane.

The high surface energy of the metal flakes used in the presentinvention enables stable dispersions in liquids to be formed, thesedispersions have a long life with little settling out.

The dispersion medium is hydrocarbon, mineral or synthetic base oil,silicone fluid or any other liquid which does not react with the metalflakes.

The amount of metal dispersed in the liquid depends on the use to whichthe dispersion is to be put, but is preferably 130% by wt. However ifthe liquid is a lubricating oil, a grease composition is formed if asufiicient quantity of the metal flakes are dispersed in the oil. Forforming a grease composition from 10% wt. to 25% of the high energy,metal flakes are usually dispersed in a mineral or synthetic base oil.

The lubricating base oil, may be a mineral or synthetic oil. Suitablemineral oils are refined mineral oils obtained from petroleum, forexample, those having a viscosity at 210 F. within the range from 2 to50 centistokes, preferably 4 to 40 centistokes.

Synthetic lubricating oils include organic esters, polyglycol ethers,polyphenyl ethers, fluorinated hydrocarbons, silicate esters, siliconeoils and mixtures thereof.

The most important class of synthetic oils are the organic liquidpolyesters, particularly the neutral polyesters, having a viscosity at210 F. within the range from 1 to 30 centistokes. The expressionpolyester is used to mean esters having at least tWo ester linkages permolecule. The expression neutral is used to mean a fully esterifiedproduct. Examples of suitable polyesters include liquid diesters ofaliphatic dicarboxylic acids and monohydric alcohols, such as, forexample, dioctyl sebacate, dinonyl sebacate, octyl nonyl sebacate, andthe corresponding azelates and adipates; liquid diesters of aliphaticdicarboxylic acids and phenols and more complex polyesters.

The finely divided metal powder can be incorporated into a grease by anumber of methods. It is preferred to incorporate the finely dividedmetal powder into a grease, immediately after grinding. However, if thefinely divided metal powder is prepared some time before incorporationinto the grease, it is preferred to store the finely divided metalpowder in an air-tight container to prevent deterioration.

The slurry of metal flakes produced in the grinding process can beconverted into a grease by, for example:

(a) The grinding liquid is filtered off. The resulting filter cake isground by, for example, feeding the cake through a colloid mill andstirring the resulting powder into the oil. The resulting grease isfinished by colloid milling.

(b) The grinding liquid is boiled off rapidly to avoid the formation ofa metal powder cake and the resulting 3 powder is stirred into the oiland the grease finished by colloid milling.

(c) Oil is added to the slurry of finely divided metal powder and thegrinding liquid distilled off.

((1) Oil is added to the slurry of finely divided metal powder and themixture circulated through a homogeniser (for example, of theManton-Gaulic type) so that temperatures up to or exceeding 140 C. areproduced. The temperature must be high enough to drive off the grindingliquid.

(e) The metal might also be ground directly in the base oil for thegrease. For example, a low boiling point, low viscosity, low surfacetension mineral lubricating oil with a viscosity up to 600 centistokesat 100 F. (38 C.) can be used. Elevated temperatures up to 400 C. can beused during the grinding.

Methods (d) and (e) are particularly preferred. In general, the finelydivided metal powders can be incorporated into the base oil either atambient temperatures or, if desired, at elevated temperatures, forexample, up to 400 C.

are nearly filled with inch diameter hardened steel balls. The mill isfitted with a Mr horsepower electric motor and the oscillation can beadjusted from 1 to 4 mm. In operation, each cylinder was filledcompletely with n-heptane containing dissolved therein the lubricatingadditive and steel balls and from 10 to 50 grams of metal powder of from50 to 400 British Standard mesh were added. The ends were then sealedwith metal caps fitted with rubber washers and grinding carried out atan oscillation of 4 mm. and a frequency 10f 3000 vibrations per minute.After grinding the balls were sieved from the slurry of metal powder andnheptane and lubricating additive and the treated metal powder recoveredby filtration, washing and drying.

Th metal powders were stirred into a 160/95 mineral base oil to form agrease which contained by weight of the metal.

The base oil used had a viscosity of 160 Redwood No. 1 secs. at 140 F.and a viscosity index of 95.

The properties of these greases are shown in the following table.

Wt. 01 Surface Surface grinding energy 1 area, Worked I additive, cals.metres Bulk penetration Unworkcd Metal Grinding additive percent wt. pergram gram density 60 strokes penetration Steel Stearie acid. 5 106 18 0.19 223 200 Aluminum Palmitie acid 5 0. 12 1 0. 19 324 298 1 Heat ofinter action of n-butanol, measured without removing any absorbedgrinding fluid.

The greases according to the invention have remarkably high Drop Points.When their drop points are measured according to the IP or ASTM standardmethods, they are found to be above 400 C.; such greases are describedas infusible and are difficult to produce by conventional methods. Byusing carefully selected base oils, for example, synthetic oils withhigh oxidation and thermal stability, greases having a uniquecombination of properties can be produced.

In certain circumstances it may be advantageous to add dispersants tothe metal either before grinding or after grinding. In this way thedispersion of the finely divided metal powders may be aided. Viscosityindex improvers, metal deactivators, anti-corrosion agents,anti-oxidants, etc., can also be added to the greases of the invention.

It has been found that the dispersions of the present invention possessload-carrying properties, and that dispersion of metal flakes inlubricating oils improve the load-carrying behaviour of the oils.

Liquids containing ferromagnetic flakes have properties which differ insome respects from liquids containing non-ferromagnetic flakes.Dispersions of iron flakes in a liquid render the whole liquidsusceptable to magnetic fields. Thus it is possible to move the bulk ofthe liquid by magnetic forces. This is also true of greases thickened byiron flakes. Grease thickened by iron flakes are also electricallyconductive. These properties of dispersions of iron flakes are veryuseful in electric power systems, transmission devices, pumps andnon-mechanical valves.

Greases thickened by iron flakes also harden upon working in contrast toordinary greases. Thus the values for penetration of the grease decreaseupon working.

The dispersions of other metals in organic liquids are useful inelectrostatic applications such as in control mechanisms, such asvalves.

EXAMPLE Various metals were ground in n-heptane containing variouslubricating additives using a Megapact mill manufactured by PilamecLimited.

In this mill the grinding chambers are steel cylinders of 1% inchesinternal diameter by 15 inches long and The grease formed by the steelflakes had a specific resistance of 45 ohms/cm.

When this grease was placed in a magnetic field the grease hardened andstiffened.

Dispersions were obtained by dispersing the metal flakes in n-heptaneand leaving them undisturbed for 24 hours. The suspensions were black incolour and contained 5% by weight of the flakes. No settling out wasobserved after this time.

When a magnetic field was applied to the suspension containing ironflakes the whole bulk of the liquid was affected and its shape wasaltered in response to the magnetic field. There was no separation ofthe iron flakes under the influence of the magnetic field.

It is very surprising that the metal flakes thicken the oils to greases,and that the liquids containing iron flakes should be renderedsusceptible to magnetic fields throughout their bulk.

What I claim is:

1. A lubricating composition consisting of a lubricating oil containingan effective amount of oleophilic metal flakes selected from metals andalloys prepared by grinding a metal selected from metals and alloys inan organic liquid distilling below 500 C., having a viscosity below 600centistokes at 38 C., and having a surface tension below 72 dynes/cm. at25 C., until said metal becomes oleophilic and has a surface area of atleast 1 square meter per gram.

2. The lubricating composition of claim 1 in the form of a grease.

3. The lubricating composition of claim 1 in the form of a dispersion.

References Cited UNITED STATES PATENTS 2,742,427 4/ 1956 Reiff 252263,180,835 4/1965 Peri 252-26 3,267,032 8/1966 Ravener 25226 3,409,54911/1968 Freeman 25226 DANIEL E. WYMAN, Primary Exaimner I. VAUGHN,Assistant Examiner

